Diagnostics of optical nonlinearities: spatial beam distortion technique and its application to semiconductors and novel materials

Development of nonlinear refraction diagnostics methods based on spatial beam distortions technique and nonlinear absorption measurements is illustrated with wide-gap semiconductors experimental data. With picosecond Z-scan technique we have studied competitive optical nonlinearities -- intraband direct equilibrium carriers transitions saturation and interband two-photon absorption (TPA) for a α-SiC(6H) crystal, and enhanced state absorption, absorption saturation and TPA -- of epoxy polymer based on diglicidyl ether of bisphenol A in a wide pumping intensities range (10 MW/cm 2 - 20 GW/cm 2 ) at 532 nm. The complexity of the analysis was dealt with the nonlinearities signatures recognition problem and selection the part of the Z-scan curve which corresponds to the dominant contribution of the proper nonlinear mechanism on the background of competitive others. The TPA coefficient is β = 3.2 ± 0.3 cm/GW for the α-SiC(6H) crystal. The TPA coefficient is β = 4.0 ± 0.5 cm/GW for the polymer. At very high laser intensities (>7 GW/cm 2 ) photoinduced transformation into some new configuration is taken place that is more absorbent at 532 nm. The TPA coefficient is β = 16.7 ± 3 cm/GW for the photoproduct. Up to pumping irradiance of 20 GW/cm 2 no optical damage of the polymer was observed.